As the others said, you should be able to stop rendering by clicking in the UI with any tool. Also consider setting a different high quality threshold in the 3D prefs to avoid lock-ups, at least while you test things. You can always switch back to a higher setting later and then give your machine enough time to render at best quality...
Some more details pointing out as a "hardware performance / software interrupt" problem bug:
On MacPro 3,1 [2x2.8GHz Xeon 16GB RAM]= no way to exit from render, no matter what you click. Only ForceQuit solve.
On Hackintosh [3.49GHZ Core i7 32GB RAM]= works OK. Stops immediately when you click.
Both same osX, same CS6 versions.
Asking for a more responsive UI feedback when in rendering. Reserve some CPU power to mouse action...
Do you get this consistently with the same file? If so is this something you can share with Adobe? We have a bug report that sounds somewhat similar, but haven't found consistent steps for reproducing the problem.
seems we posted at same time.
Here seems an hardware CPU-power related item. No problem to send my .PSD file.
BTW was like that in previous Photoshop version: when in raytracing no way to stop it on MacPro 3,1
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